The contryphans, a D-tryptophan-containing family of Conus peptides: interconversion between conformers

We previously characterized contryphan-R, a D-tryptophan-containing octapeptide from the venom of Conus radiatus. In this study, we present evidence that the contryphan family of peptides is widely distributed in venoms of the fish-hunting cone snails. We purified, synthesized and characterized contryphan-Sm from Conus stercusmuscarum venom, and obtained molecular evidence for the existence of a third peptide, contryphan-P from Conus purpurascens venom ducts. The sequences of these three contryphans showed identity in seven of eight amino acids and a conserved pattern of post-translational modification. We also demonstrate that contryphan-Sm equilibrates between two distinct conformational states.

A novel post-translational modification involving bromination of tryptophan. Identification of the residue, L-6-bromotryptophan, in peptides from Conus imperialis and Conus radiatus venom

We report a novel post-translational modification involving halogenation of tryptophan in peptides recovered from the venom of carnivorous marine cone snails (Conus). The residue, L-6-bromotryptophan, was identified in the sequence of a heptapeptide, isolated from Conus imperialis, a worm-hunting cone. This peptide does not elicit gross behavioral symptoms when injected centrally or peripherally in mice. L-6-Bromotryptophan was also identified in a 33-amino acid peptide from Conus radiatus; this peptide has been shown to induce a sleep-like state in mice of all ages and is referred to as bromosleeper peptide. The sequences of the two peptides and were determined using a combination of mass spectrometry, amino acid, and chemical sequence analyses, where Pca = pyroglutamic acid, Hyp = hydroxyproline, Gla = gamma-carboxyglutamate, and Trp* = L-6-bromotryptophan. The precise structure and stereochemistry of the modified residue were determined as L-6-bromotryptophan by synthesis, co-elution, and enzymatic hydrolysis experiments. To our knowledge this is the first documentation of tryptophan residues in peptides/proteins being modified in a eukaryotic system and the first report of halogenation of tryptophan in vivo.

Bromocontryphan: post-translational bromination of tryptophan

We demonstrate that post-translational bromination of a tryptophan residue occurs in the biologically active octapeptide bromocontryphan, purified and characterized from Conus radiatus venom. Clones encoding bromocontryphan were identified from a cDNA library made from C. radiatus venom ducts. The mRNA sequence obtained predicts a prepropeptide which has the mature peptide sequence at the C-terminal end, with the L-6-bromotryptophan residue encoded by UGG, the Trp codon. These data provide the first direct evidence for post-translational bromination of a polypeptide which is translated through the normal cellular machinery. In addition to bromination, the peptide, which induces a "stiff tail" syndrome in mice, has several other modifications as shown by the sequence [Formula: See Text] in which Hyp = hydroxyproline. Asterisks indicate post-translational modifications (left to right): proteolytic cleavage at the N-terminus; hydroxylation of Pro3; epimerization of Trp4; bromination of Trp7, and C-terminal amidation. Bromocontryphan appears to have the highest density of post-translational modifications known among gene-encoded polypeptides. The overall result is a molecule which closely resembles marine natural products produced through specialized biosynthetic pathways comprising many enzyme-catalyzed steps.

Contryphan is a D-tryptophan-containing Conus peptide

In this report, we document for the first time the occurrence of D-tryptophan in a normally translated polypeptide, contryphan. The peptide, isolated from the venom of the fish-hunting marine snail Conus radiatus, produces the "stiff-tail" syndrome in mice. Characterization of the octapeptide gave the following sequence, Gly-Cys-Hyp-D-Trp-Glu-Pro-Trp-Cys-NH2 where Hyp = 4-trans-hydroxyproline. The presence of D-tryptophan in position 4 of contryphan was confirmed by chemical synthesis. The post-translational epimerization in all other D-amino acid-containing small peptides characterized previously from vertebrates and molluscan systems is in position 2.

A new family of Conus peptides targeted to the nicotinic acetylcholine receptor

In this work, a new family of Conus peptides, the alpha A-conotoxins, which target the nicotinic acetylcholine receptor, is defined. The first members of this family have been characterized from the eastern Pacific species, Conus purpurascens (the purple cone); three peptides that cause paralysis in fish were purified and characterized from milked venom. The sequence and disulfide bonding pattern of one of these, alpha A-conotoxin PIVA, is as follows: [formula: see text] where O represents trans-4-hydroxyproline. The two other peptides purified from C. purpurascens venom are the under-hydroxylated derivatives, [Pro13]alpha A-conotoxin PIVA and [Pro7,13]alpha A-conotoxin PIVA. The peptides have been chemically synthesized in a biologically active form. Both electrophysiological experiments and competition binding with alpha-bungarotoxin demonstrate that alpha A-PIVA acts as an antagonist of the nicotinic acetylcholine receptor at the postsynaptic membrane.

Delta-conotoxin GmVIA, a novel peptide from the venom of Conus gloriamaris

A novel peptide toxin, delta-conotoxin GmVIA, was purified from the venom of Conus gloriamaris, a mollusc-hunting snail. It consists of 29 amino acids, including six Cys residues: [sequence: see text] The pattern of disulfide connectivity (4-19, 12-24, and 18-29) is the same as for the omega-conotoxins, which are Ca2+ channel ligands. However, the peptide does not compete with omega-conotoxin for binding to membrane preparations from frog, rat, and chick brain. Instead, initial electrophysiological results suggest that the peptide induces action potential broadening in molluscan neurons by slowing down Na+ current inactivation. Synthetic delta-conotoxin GmVIA was prepared by solid-phase methods and appeared identical in all respects to the natural material. The chromatographic behavior of native and reduced delta-conotoxins is quite remarkable, suggesting that the disulfides form a core which forces hydrophobic residues to point out toward the solvent.

A new Conus peptide ligand for mammalian presynaptic Ca2+ channels

Voltage-sensitive Ca2+ channels that control neurotransmitter release are blocked by omega-conotoxin (omega-CgTx) GVIA from the marine snail Conus geographus, the most widely used inhibitor of neurotransmitter release. However, many mammalian synapses are omega-CgTx-GVIA insensitive. We describe a new Conus peptide, omega-CgTx-MVIIC, that is an effective inhibitor of omega-CgTx-GVIA-resistant synaptic transmission. Ca2+ channel targets that are inhibited by omega-CgTx-MVIIC but not by omega-CgTx-GVIA include those mediating depolarization-induced 45Ca2+ uptake in rat synaptosome preparations, "P" currents in cerebellar Purkinje cells, and a subset of omega-CgTx-GVIA-resistant currents in CA1 hippocampal pyramidal cells. The characterization of omega-CgTx-MVIIC by a combination of molecular genetics and chemical synthesis defines a general approach for obtaining ligands with novel receptor subtype specificity from Conus.

Conus Peptides: Phylogenetic Range of Biological Activity

The major function of the venoms of the predatory marine snails belonging to the genus Conus is to paralyze prey. Thus, the venom of each Conus species acts on receptors and ion channels of the prey; previous studies suggested much less activity on homologous receptor targets in more distant taxa. In this article, we address the question of whether some peptide components of Conus venoms ("conopeptides") have "cross-phylum" biological activity. We examined the venom of Conus textile, a mollusk-hunting Conus, using a mammalian biological activity assay. We purified a 23 amino acid "convulsant peptide" with potent activity in the mammalian CNS, even though it comes from the venom of a snail-hunting Conus species. A survey of Conus textile venom fractions indicates that, in addition to the convulsant peptide, many other components of this venom will exhibit "cross-phylum" biological activity. Conopeptides with broad-range phylogenetic specificity should be useful tools for studying the evolution of receptors and ion channels, and of nervous systems.

alpha-Conotoxins, small peptide probes of nicotinic acetylcholine receptors

alpha-Conotoxins, a family of small peptides from the venoms of the Conus marine moluscs, are selective, snake alpha-neurotoxin-competitive antagonists of the nicotinic acetylcholine receptor. A new alpha-conotoxin, SIA, has been purified, sequenced, and synthesized. Cross-linking with bivalent reagents and photoaffinity labeling of the acetylcholine receptor with alpha-conotoxin yield covalent adducts. Surprisingly, cross-linking to other subunits is considerably more efficient than to the alpha subunit. The relative efficiency of photoactivatable cross-linking to different subunits of the receptor is a function of placement of the photoactivatable group on the toxin. Since the structures of alpha-conotoxins can be solved by 2D NMR [see Pardi et al. (1989) Biochemistry 28, 5494-5508; Kobayashi et al. (1989) Biochemistry 28, 4853-4860], this family of toxins should provide a set of new ligands for probing the acetylcholine receptor with considerable precision.

Conantokin-G: a novel peptide antagonist to the N-methyl-D-aspartic acid (NMDA) receptor

Conantokin-G is a 17 amino acid peptide isolated from the venom of the fish-eating snail Conus geographus which produces hyperactivity when injected into the brains of adult mice. We show that this peptide is a selective N-methyl-D-aspartate (NMDA) antagonist based on its ability to block NMDA-induced elevation of cGMP in rat cerebellar slices in vitro (IC50 = 171 nM), but not kainic acid-induced elevations. This inhibition could not be overcome by increasing the NMDA concentration, indicating non-competitive inhibition. Conantokin-G displayed no affinity for binding sites for thienylcyclohexylpiperidine, various glutamate subclasses or those for several other neurotransmitters/neuromodulators. This peptide, however, enhanced [3H]glycine binding to rat forebrain membranes but not to spinal cord membranes. The activity profile of the peptide in various assays indicates that it is a novel type of non-competitive NMDA antagonist.

Diversity of Conus neuropeptides

Conus venoms contain a remarkable diversity of pharmacologically active small peptides. Their targets are ion channels and receptors in the neuromuscular system. The venom of Conus geographus contains high-affinity peptides that act on voltage-sensitive calcium channels, sodium channels, N-methyl-D-aspartate (NMDA) receptors, acetylcholine receptors, and vasopressin receptors; many more peptides with still uncharacterized receptor targets are present in this venom. It now seems that the Conus species (approximately 500 in number) will each use a distinctive assortment of peptides and that the pharmacological diversity in Conus venoms may be ultimately comparable to that of plant alkaloids or secondary metabolites of microorganisms. The cone snails may generate this diverse spectrum of venom peptides by a "fold-lock-cut" synthetic pathway. These peptides are specific enough to discriminate effectively between closely related receptor subtypes and can be used for structure-function correlations.

Conantokin-T. A gamma-carboxyglutamate containing peptide with N-methyl-d-aspartate antagonist activity

Conantokin-T, a 21-amino acid peptide which induces sleep-like symptoms in young mice was purified from the venom of the fish-hunting cone snail, Conus tulipa. The amino acid sequence of the peptide was determined and verified by chemical synthesis. The peptide has 4 residues of the modified amino acid, gamma-carboxyglutamate (Gla). The sequence of the peptide is: Gly-Glu-Gla-Gla-Tyr-Gln-Lys-Met-Leu-Gla-Asn-Leu-Arg-Gla-Ala-Glu-Val-Lys- Lys-Asn-Ala-NH2. Conantokin-T inhibits N-methyl-D-aspartate (NMDA) receptor-mediated calcium influx in central nervous system neurons. This observation suggests that like conantokin-G (a homologous Conus peptide with recently identified NMDA antagonist activity) conantokin-T has NMDA antagonist activity. A sequence comparison of conantokins-T and -G identifies the 4 Gla residues and the N-terminal dipeptide sequence as potential key elements for the biological activity of this peptide.

Constant and hypervariable regions in conotoxin propeptides

Conotoxins are small cysteine rich peptides found in the venom of the predatory cone snails (Conus) which have prove to be useful high affinity ligands for various receptors and ion channels. The first cloning data for conotoxins, reported here, were obtained for the King-Kong peptide, a 27 amino acid conotoxin found in the venom of the cloth-of-gold cone, Conus textile. Analysis of cDNA clones of the King-Kong peptide revealed a family of related toxin transcripts. Three different propeptide cDNA sequences were obtained; only one of these encoded sequence for the King-Kong peptide. The other cDNA sequences encoded two different peptides (KK-1 and KK-2). When the predicted propeptide sequences are compared, well defined conserved and hypervariable regions can be identified. The hypervariable regions comprise four regions between Cys residues in the final peptide toxins; the remainder of the propeptide sequences, i.e. the excised N-terminal regions and the disulfide bonded Cys residues, are highly conserved. We suggest that the conserved regions may direct the formation of a specific disulfide configuration in the King-Kong family of conotoxins.

mu-conotoxin GIIIA, a peptide ligand for muscle sodium channels: chemical synthesis, radiolabeling, and receptor characterization

The peptide conotoxin GIIIA from Conus geographus L. venom, which specifically blocks sodium channels in muscle, has been synthesized by a solid-phase method. The three disulfide bridges were formed by air oxidation. After HPLC purification, the synthetic product was shown to be identical with the native conotoxin GIIIA from Conus geographus. A high specific activity, 125I derivative of mu-conotoxin was prepared and used for binding assays to the Na channel from Electrophorus electric organ. Specific binding could be abolished by competition with tetrodotoxin. The radiolabeled toxin was specifically cross-linked to the Na channel. These studies demonstrate that mu-conotoxin GIIIA can be used to define the guanidinium toxin binding site and will be a useful ligand for understanding functionally important differences between Na channel subtypes.

A molluscivorous Conus toxin: conserved frameworks in conotoxins

We purified and characterized a 27 amino acid toxin from a snail-hunting Conus venom, Conus textile. This toxin causes convulsive-like activity in snails and causes subordinate lobsters to assume an exaggerated dominant posture. The sequence of this peptide is Trp-Cys-Lys-Gln-Ser-Gly-Glu-Met-Cys-Asn-Leu-Leu-Asp-Gln-Asn-Cys-Cys-Asp- Gly-Tyr-Cys-Ile-Val-Leu-Val-Cys-Thr. The sequence was confirmed by determining the nucleotide sequence of a cDNA clone coding for the peptide. The conservation of Cys residues compared to the omega-conotoxins from piscivorous Conus venom suggests that toxins from different cone venoms may use only a few "Cys-motifs" as conserved structural backbones for targeting to a variety of receptors in different animals.

Phylogenetic specificity of cholinergic ligands: alpha-conotoxin SI

The alpha-conotoxins are small peptide neurotoxins from the venom of fish-hunting cone snails which block nicotinic acetylcholine receptors (nAChRs). We describe the purification, characterization, and chemical synthesis of a new alpha-conotoxin from Conus striatus, alpha-conotoxin SI. In contrast to other AChR ligands, alpha-SI discriminates between different vertebrate nAChRs. The sequence of alpha-conotoxin SI is Ile-Cys-Cys-Asn-Pro5-Ala-Cys-Gly-Pro-Lys10-Tyr-Ser-Cys-NH2. This sequence was confirmed by chemical synthesis. A des-Ile-alpha-SI derivative was also synthesized and is biologically active. Although alpha-conotoxin SI is highly homologous to previously described alpha-conotoxins, it has one noteworthy sequence feature which may account for its novel biological specificity. In all other alpha-conotoxins, there is a positively charged amino acid at residue 9; in alpha-conotoxin SI, this is replaced by proline. The discovery that different alpha-conotoxins can vary by orders of magnitude in their apparent affinity for different vertebrate receptors demonstrates that alpha-conotoxins will be useful probes for investigating phylogenetic differences between vertebrate nAChRs.

Total synthesis and further characterization of the gamma-carboxyglutamate-containing "sleeper" peptide from Conus geographus venom

The total synthesis of the Gla-containing "sleeper" peptide (Gly-Glu-Gla-Gla-Leu-Gln-Gla-Asn-Gln-Gla-Leu-Ile-Arg-Gla-Lys-Ser-Asn-NH2 ) from Conus geographus is described. A new strategy for the synthesis of acid-sensitive peptide amides was developed, which allowed complete deprotection and cleavage of the L-gamma-carboxyglutamate-containing peptide from the 2,4-dimethoxybenzhydrylamine resin. Synthetic sleeper peptide, after preparative high-performance liquid chromatography (HPLC) purification, was shown to be identical with the native peptide by all criteria (coelution experiments of HPLC, sequence analysis, and biological activity). In addition, a developmental switch in the behavioral symptoms induced by the peptide after intracerebral administration in mice was documented. At low doses of the peptide (4-30 pmol/g), a sleeplike state was induced in mice under 2 weeks old; in contrast, older mice became markedly hyperactive. It is proposed that, in the presence of Ca2+, the sleeper peptide assumes an alpha-helical configuration in which all the gamma-carboxyglutamate residues are located on the same side of the alpha-helix.

Invertebrate vasopressin/oxytocin homologs. Characterization of peptides from Conus geographus and Conus straitus venoms

The vasopressin-oxytocin family of peptides is of very ancient lineage, found in organisms as diverse as hydra and man. Although these peptides have been intensively studied in vertebrates, the presumably more extensive invertebrate series was defined primarily by immunological methods. In this report, we describe the purification and structures of two peptides of the vasopressin-oxytocin family from molluscs ("Conopressins"), which were found in the venom of fish-hunting marine snails of the genus Conus. The biological activity observed when the two snail peptides are injected intracerebrally into mice is very similar to that elicited by the vertebrate neurohypophyseal hormones and presumably reflects their actions upon a common receptor in the brain. The sequences of the purified peptides reveal unique features not found in the vertebrate peptide series, most notably an additional positive charge. These are the first members of the invertebrate series of the vasopressin-oxytocin family to be characterized biochemically. The sequences of these peptides are: from Conus geographus venom, Lys-conopressin-G, Cys-Phe-Ile-Arg-Asn-Cys-Pro-Lys-Gly-NH2; and from Conus striatus venom, Arg-conopressin-S, Cys-Ile-Ile-Arg-Asn-Cys-Pro-Arg-Gly-NH2.

Transmitter release from presynaptic terminals of electric organ: inhibition by the calcium channel antagonist omega Conus toxin

Cholinergic synaptosomes from electroplax of the ray Ommata discopyge release both ATP and ACh when depolarized with high K+ concentration in the presence of Ca2+. Others have shown that the ATP and ACh are released in the molar ratio found in isolated synaptic vesicles. Thus, it is assumed that the release of ATP reflects exocytosis of synaptic vesicles, and that transmitter release can be indirectly monitored by assaying ATP release. We present further evidence for this assumption and examine the effects of presynaptic neurotoxins on this ATP release. As expected for transmitter release, we find that depolarization-evoked ATP release is supported by Sr2+ and Ba2+ and is inhibited by the Ca channel antagonists Co2+ and Mn2+. Likewise, the presynaptic toxins omega-CmTX and omega-CgTX, omega peptides from the venom of the marine snails Conus magus and Conus geographus, respectively, inhibit 80% of the depolarization-evoked ATP release. Half-maximal inhibition of ATP release occurs with approximately 0.5 microM of either toxin. The toxins' effects are reversible, and when toxin is washed away, the time dependence of recovery of release is approximately first order and half complete within 40 min with omega-CmTX and 15 min with omega-CgTX. The Ca2+ ionophore A23187 induces Ca2+-dependent ATP release from resting synaptosomes. As would be expected of a Ca channel antagonist, omega-CmTX does not affect this ionophore-induced release. Leptinotarsin-d (LPTd), a putative Ca channel agonist from the Colorado potato beetle, evokes Ca2+-dependent ATP release from resting synaptosomes. omega-CmTX does not block LPTd-evoked release of ATP, which suggests that omega-CmTX and LPTd act at different sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Omega-conotoxin: direct and persistent blockade of specific types of calcium channels in neurons but not muscle

Blockade of Ca2+ channels by omega-conotoxin GVIA, a 27 amino acid peptide from the venom of the marine snail Conus geographus, was investigated with patch-clamp recordings of whole-cell and unitary currents in a variety of cell types. In dorsal root ganglion neurons, the toxin produces persistent block of L- and N-type Ca2+ channels but only transiently inhibits T-type channels. Its actions appear to be neuron-specific, since it blocks high-threshold Ca2+ channels in sensory, sympathetic, and hippocampal neurons of vertebrates but not in cardiac, skeletal, or smooth muscle cells. Block occurs through direct interaction of the toxin with an external site closely associated with the Ca2+ channel, without apparent involvement of a second messenger or dependence on channel gating. The tissue and channel-type specificity and the directness and slow reversibility of the block are features that favor use of omega-conotoxin as a tool for purifying particular neuronal Ca2+ channels and defining their physiological function.

Neuronal calcium channel antagonists. Discrimination between calcium channel subtypes using omega-conotoxin from Conus magus venom

The omega-conotoxins from the venom of fish-hunting cone snails are probably the most useful of presently available ligands for neuronal Ca channels from vertebrates. Two of these peptide toxins, omega-conotoxins MVIIA and MVIIB from the venom of Conus magus, were purified. The amino acid sequences show significant differences from omega-conotoxins from Conus geographus. Total synthesis of omega-conotoxin MVIIA was achieved, and biologically active radiolabeled toxin was produced by iodination. Although omega-conotoxins from C. geographus (GVIA) and C. magus (MVIIA) appear to compete for the same sites in mammalian brain, in amphibian brain the high-affinity binding of omega-conotoxin MVIIA has narrower specificity. In this system, it is demonstrated that a combination of two omega-conotoxins can be used for biochemically defining receptor subtypes and suggested that these correspond to subtypes of neuronal Ca2+ channels.